Natural gas liquid fractionation plant waste heat conversion to power using dual turbines organic Rankine cycle

ABSTRACT

Certain aspects of a natural gas liquid fractionation plant waste heat conversion to power using dual turbines Organic Rankine Cycle can be implemented as a first heating fluid circuit thermally coupled to first multiple heat sources of a natural gas liquid (NGL) fractionation plant, a second heating fluid circuit thermally coupled to second multiple heat sources of the NGL fractionation plant, and two power generation systems, each including an organic Rankine cycle (ORC). A control system actuates a first set of control valves to selectively thermally couple the first heating fluid circuit to at least a portion of the first multiple heat sources of the NGL fractionation plant, and to actuate a second set of control valves to selectively thermally couple the second heating fluid circuit to at least a portion of the second multiple heat sources of the NGL fractionation plant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims the benefit of priority to U.S. Application Ser.No. 62/542,687 entitled “Utilizing Waste Heat Recovered From Natural GasLiquid Fractionation Plants,” which was filed on Aug. 8, 2017, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to operating industrial facilities, for example,a natural gas liquid fractionation plant or other industrial facilitiesthat include operating plants that generate heat, for example, a naturalgas liquid fractionation plant.

BACKGROUND

Natural gas liquid (NGL) processes are chemical engineering processesand other facilities used in petroleum refineries to transform naturalgas into products, for example, liquefied petroleum gas (LPG), gasoline,kerosene, jet fuel, diesel oils, fuel oils, and such products. NGLfacilities are large industrial complexes that involve many differentprocessing units and auxiliary facilities, for example, utility units,storage tanks, and such auxiliary facilities. Each refinery can have itsown unique arrangement and combination of refining processes determined,for example, by the refinery location, desired products, economicconsiderations, or such factors. The NGL processes that are implementedto transform the natural gas into the products such as those listedearlier can generate heat, which may not be reused, and byproducts, forexample, greenhouse gases (GHG), which may pollute the atmosphere. It isbelieved that the world's environment has been negatively affected byglobal warming caused, in part, due to the release of GHG into theatmosphere.

SUMMARY

This specification describes technologies relating to cooling capacitygeneration, power generation or potable water production from waste heatin a natural gas liquid (NGL) fractionation plant.

The present disclosure includes one or more of the following units ofmeasure with their corresponding abbreviations, as shown in Table 1:

TABLE 1 Unit of Measure Abbreviation Degrees Celsius ° C. Megawatts MWOne million MM British thermal unit Btu Hour hr. or H Pounds per squareinch (pressure) psi Kilogram (mass) Kg Second S Cubic meters per daym³/day Fahrenheit F.

In a general implementation, a system includes a first heating fluidcircuit thermally coupled to first multiple heat sources of a naturalgas liquid (NGL) fractionation plant; a second heating fluid circuitthermally coupled to second multiple heat sources of the NGLfractionation plant; a first power generation system that includes afirst organic Rankine cycle (ORC), which includes (i) a first portion ofa working fluid that is thermally coupled to the first heating fluidcircuit to heat the first portion of the working fluid, and (ii) a firstexpander configured to generate electrical power from the heated firstportion of the working fluid; a second power generation system thatincludes a second organic Rankine cycle (ORC), which includes (i) asecond portion of the working fluid that is thermally coupled to thefirst and second heating fluid circuits to heat the second portion ofthe working fluid, and (ii) a second expander configured to generateelectrical power from the heated second portion of the working fluid;and a control system configured to actuate a first set of control valvesto selectively thermally couple the first heating fluid circuit to atleast a portion of the first multiple heat sources of the NGLfractionation plant, and to actuate a second set of control valves toselectively thermally couple the second heating fluid circuit to atleast a portion of the second multiple heat sources of the NGLfractionation plant.

In an aspect combinable with the general implementation, the firstportion of the working fluid is thermally coupled to the first heatingfluid circuit in an evaporator of the first ORC.

In another aspect combinable with any of the previous aspects, thesecond portion of the working fluid is thermally coupled to the firstand second heating fluid circuits in an evaporator of the second ORC.

In another aspect combinable with any of the previous aspects, Thesystem includes a heating fluid tank that is fluidly coupled to theevaporators of the first and second ORCs.

In another aspect combinable with any of the previous aspects, theworking fluid includes isobutene.

In another aspect combinable with any of the previous aspects, the firstand second heating fluid circuits include water or oil.

In another aspect combinable with any of the previous aspects, thesystem includes a condenser fluidly coupled to the first and secondexpanders and to a condenser fluid source to cool the working fluid, afirst pump to circulate the first portion of the working fluid throughthe first ORC, a second pump to circulate the second portion of theworking fluid through the second ORC.

In another aspect combinable with any of the previous aspects, the firstmultiple heat sources include a first portion of sub-units of the NGLfractionation plant that includes an ethane system, a second multiplesub-units of the NGL fractionation plant that includes a propane system,a third portion of sub-units of the NGL fractionation plant thatincludes a butane system, a fourth portion of sub-units of the NGLfractionation plant that includes a natural gasoline system, and a fifthportion of sub-units of the NGL fractionation plant that includes asolvent regeneration system.

In another aspect combinable with any of the previous aspects, the firstportion of sub-units of the NGL fractionation plant includes at leastone ethane system heat source including a first ethane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of an ethane dryer.

In another aspect combinable with any of the previous aspects, thesecond portion of sub-units of the NGL fractionation plant includes atleast three propane system heat sources including a first propane systemheat source that includes a heat exchanger that is thermally coupled toan outlet stream of a propane dehydrator, a second propane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a propane vapor recovery compressor stream, a thirdpropane system heat source that includes a heat exchanger that isthermally coupled to an outlet stream of a propane main compressorstream.

In another aspect combinable with any of the previous aspects, the thirdportion of sub-units of the NGL fractionation plant includes at leasttwo butane system heat sources including a first butane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a butane dehydrator, and a second butane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a debutanizer bottoms.

In another aspect combinable with any of the previous aspects, thefourth portion of sub-units of the NGL fractionation plant includes atleast two natural gasoline system heat sources including a first naturalgasoline system heat source that includes a heat exchanger that isthermally coupled to an outlet stream of a natural gasoline decolorizeroverhead stream, and a second natural gasoline system heat source thatincludes a heat exchanger that is thermally coupled to an outlet streamof a Reid vapor pressure control column overhead stream.

In another aspect combinable with any of the previous aspects, the fifthportion of sub-units of the NGL fractionation plant includes at leasttwo solvent regeneration system heat sources including a first solventregeneration system heat source that includes a heat exchanger that isthermally coupled to an outlet stream of an ADIP regeneration sectionoverhead stream, and a second solvent regeneration system heat sourcethat includes a heat exchanger that is thermally coupled to an outletstream of an ADIP regeneration section bottoms.

In another aspect combinable with any of the previous aspects, thesecond multiple heat sources include a first portion of sub-units of theNGL fractionation plant that includes an ethane system, a secondmultiple sub-units of the NGL fractionation plant that includes apropane system, a third portion of sub-units of the NGL fractionationplant that includes a butane system, a fourth portion of sub-units ofthe NGL fractionation plant that includes a pentane system, and a fifthportion of sub-units of the NGL fractionation plant that includes anatural gasoline system.

In another aspect combinable with any of the previous aspects, the firstportion of sub-units of the NGL fractionation plant includes at leastone ethane system heat source including a first ethane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a deethanizer refrigeration compressor.

In another aspect combinable with any of the previous aspects, thesecond portion of sub-units of the NGL fractionation plant includes atleast two propane system heat sources including a first propane systemheat source that includes a heat exchanger that is thermally coupled toan outlet stream of a depropanizer overhead stream, and a second propanesystem heat source that includes a heat exchanger that is thermallycoupled to an outlet stream of a propane refrigeration compressorstream.

In another aspect combinable with any of the previous aspects, the thirdportion of sub-units of the NGL fractionation plant includes at leasttwo butane system heat sources that includes a first butane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a debutanizer overhead stream, and a second butanesystem heat source that includes a heat exchanger that is thermallycoupled to an outlet stream of a butane refrigeration compressor stream.

In another aspect combinable with any of the previous aspects, thefourth portion of sub-units of the NGL fractionation plant includes atleast one pentane system heat source including a first pentane systemheat source that includes a heat exchanger that is thermally coupled toan outlet stream of a depentanizer overhead stream.

In another aspect combinable with any of the previous aspects, the fifthportion of sub-units of the NGL fractionation plant includes at leastone natural gasoline system heat source including a first naturalgasoline system heat source that comprises a heat exchanger that isthermally coupled to an outlet stream of a natural gasoline decolorizingsection pre-flash drum overhead stream.

In another general implementation, a method of recovering heat energygenerated by a NGL fractionation plant includes circulating a firstheating fluid through a first heating fluid circuit thermally coupled tofirst multiple heat sources of a natural gas liquid (NGL) fractionationplant; circulating a second heating fluid is circulated through a secondheating fluid circuit thermally coupled to a second plurality of heatsources of the NGL fractionation plant; generating electrical powerthrough a first power generation system that includes a first organicRankine cycle (ORC), which includes (i) a first portion of a workingfluid that is thermally coupled to the first heating fluid circuit toheat the first portion of the working fluid, and (ii) a first expanderconfigured to generate electrical power from the heated first portion ofthe working fluid; generating electrical power is generated through asecond power generation system that includes a second organic Rankinecycle (ORC), which includes (i) a second portion of the working fluidthat is thermally coupled to the first and second heating fluid circuitsto heat the second portion of the working fluid, and (ii) a secondexpander configured to generate electrical power from the heated secondportion of the working fluid; actuating, with a control system, a firstset of control valves to selectively thermally couple the first heatingfluid circuit to at least a portion of the first multiple heat sourcesof the NGL fractionation plant; and actuating, with the control system,a second set of control valves to selectively thermally couple thesecond heating fluid circuit to at least a portion of the secondmultiple heat sources of the NGL fractionation plant.

In an aspect combinable with the general implementation, the firstportion of the working fluid is thermally coupled to the first heatingfluid circuit in an evaporator of the first ORC.

In another aspect combinable with any of the previous aspects, Thesecond portion of the working fluid is thermally coupled to the firstand second heating fluid circuits in an evaporator of the second ORC.

In another aspect combinable with any of the previous aspects, thesystem includes a heating fluid tank that is fluidly coupled to theevaporators of the first and second ORCs.

In another aspect combinable with any of the previous aspects, theworking fluid includes isobutene.

In another aspect combinable with any of the previous aspects, the firstand second heating fluid circuits include water or oil.

In another aspect combinable with any of the previous aspects, thesystem includes a condenser fluidly coupled to the first and secondexpanders and to a condenser fluid source to cool the working fluid, afirst pump to circulate the first portion of the working fluid throughthe first ORC, a second pump to circulate the second portion of theworking fluid through the second ORC.

In another aspect combinable with any of the previous aspects, the firstmultiple heat sources include a first portion of sub-units of the NGLfractionation plant that includes an ethane system, a second multiplesub-units of the NGL fractionation plant that includes a propane system,a third portion of sub-units of the NGL fractionation plant thatincludes a butane system, a fourth portion of sub-units of the NGLfractionation plant that includes a natural gasoline system, and a fifthportion of sub-units of the NGL fractionation plant that includes asolvent regeneration system.

In another aspect combinable with any of the previous aspects, the firstportion of sub-units of the NGL fractionation plant includes at leastone ethane system heat source including a first ethane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of an ethane dryer.

In another aspect combinable with any of the previous aspects, thesecond portion of sub-units of the NGL fractionation plant includes atleast three propane system heat sources including a first propane systemheat source that includes a heat exchanger that is thermally coupled toan outlet stream of a propane dehydrator, a second propane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a propane vapor recovery compressor stream, a thirdpropane system heat source that includes a heat exchanger that isthermally coupled to an outlet stream of a propane main compressorstream.

In another aspect combinable with any of the previous aspects, the thirdportion of sub-units of the NGL fractionation plant includes at leasttwo butane system heat sources including a first butane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a butane dehydrator, and a second butane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a debutanizer bottoms.

In another aspect combinable with any of the previous aspects, thefourth portion of sub-units of the NGL fractionation plant includes atleast two natural gasoline system heat sources including a first naturalgasoline system heat source that includes a heat exchanger that isthermally coupled to an outlet stream of a natural gasoline decolorizeroverhead stream, and a second natural gasoline system heat source thatincludes a heat exchanger that is thermally coupled to an outlet streamof a Reid vapor pressure control column overhead stream.

In another aspect combinable with any of the previous aspects, the fifthportion of sub-units of the NGL fractionation plant includes at leasttwo solvent regeneration system heat sources including a first solventregeneration system heat source that includes a heat exchanger that isthermally coupled to an outlet stream of an ADIP regeneration sectionoverhead stream, and a second solvent regeneration system heat sourcethat includes a heat exchanger that is thermally coupled to an outletstream of an ADIP regeneration section bottoms.

In another aspect combinable with any of the previous aspects, thesecond multiple heat sources include a first portion of sub-units of theNGL fractionation plant that includes an ethane system, a secondmultiple sub-units of the NGL fractionation plant that includes apropane system, a third portion of sub-units of the NGL fractionationplant that includes a butane system, a fourth portion of sub-units ofthe NGL fractionation plant that includes a pentane system, and a fifthportion of sub-units of the NGL fractionation plant that includes anatural gasoline system.

In another aspect combinable with any of the previous aspects, the firstportion of sub-units of the NGL fractionation plant includes at leastone ethane system heat source including a first ethane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a deethanizer refrigeration compressor.

In another aspect combinable with any of the previous aspects, thesecond portion of sub-units of the NGL fractionation plant includes atleast two propane system heat sources including a first propane systemheat source that includes a heat exchanger that is thermally coupled toan outlet stream of a depropanizer overhead stream, and a second propanesystem heat source that includes a heat exchanger that is thermallycoupled to an outlet stream of a propane refrigeration compressorstream.

In another aspect combinable with any of the previous aspects, the thirdportion of sub-units of the NGL fractionation plant includes at leasttwo butane system heat sources that includes a first butane system heatsource that includes a heat exchanger that is thermally coupled to anoutlet stream of a debutanizer overhead stream, and a second butanesystem heat source that includes a heat exchanger that is thermallycoupled to an outlet stream of a butane refrigeration compressor stream.

In another aspect combinable with any of the previous aspects, thefourth portion of sub-units of the NGL fractionation plant includes atleast one pentane system heat source including a first pentane systemheat source that includes a heat exchanger that is thermally coupled toan outlet stream of a depentanizer overhead stream.

In another aspect combinable with any of the previous aspects, the fifthportion of sub-units of the NGL fractionation plant includes at leastone natural gasoline system heat source including a first naturalgasoline system heat source that comprises a heat exchanger that isthermally coupled to an outlet stream of a natural gasoline decolorizingsection pre-flash drum overhead stream.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the detailed description. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a dual organic Rankine cycle (ORC) based wasteheat to power conversion plant that uses waste heat from one or moreheat sources in a NGL fractionation plant.

FIG. 1B is a diagram of deethanizer section waste heat recovery systemin a NGL plant.

FIG. 1C is a diagram of a propane dehydrator section waste heat recoverysystem in a NGL plant.

FIG. 1D is a diagram of a depropanizer section waste heat recoverysystem in a NGL plant.

FIG. 1E is a diagram of a butane dehydrator section waste heat recoverysystem in a NGL plant.

FIG. 1F is a diagram of a debutanizer section waste heat recovery systemin a NGL plant.

FIG. 1G is a diagram of a depentanizer section waste heat recoverysystem in a NGL plant.

FIG. 1H is a diagram of a solvent regeneration section waste heatrecovery system in a NGL plant.

FIG. 1I is a diagram of a natural gasoline decolorizing section wasteheat recovery system in a NGL plant.

FIG. 1J is a diagram of a propane tank recovery section waste heatrecovery system in a NGL plant.

FIG. 1K is a diagram of propane product refrigeration section waste heatrecovery system in a NGL plant.

FIG. 1L is a diagram of propane product sub-cooling section waste heatrecovery system in a NGL plant.

FIG. 1M is a diagram of butane product refrigeration section waste heatrecovery system in a NGL plant.

FIG. 1N is a diagram of ethane production section waste heat recoverysystem in a NGL plant.

FIG. 1O is a diagram of natural gasoline vapor section waste heatrecovery system in a NGL plant.

DETAILED DESCRIPTION

NGL Plant

Gas processing plants can purify raw natural gas or crude oil productionassociated gases (or both) by removing common contaminants such aswater, carbon dioxide and hydrogen sulfide. Some of the substances whichcontaminate natural gas have economic value and can be processed or soldor both. Upon the separation of methane gas, which is useful as salesgas for houses and power generation, the remaining hydrocarbon mixturein liquid phase is called natural gas liquids (NGL). The NGL isfractionated in a separate plant or sometimes in the same gas processingplant into ethane, propane and heavier hydrocarbons for severalversatile uses in chemical and petrochemical as well as transportationindustries. The NGL fractionation plant uses the following processes orsections: fractionation, product treating, and natural gasolineprocessing. The fractionation processes or sections can include heatsources (also commonly referred to as streams) including, but notlimited to, a propane condenser, a propane refrigerant condenser, anaphtha cooler, a depentanizer condenser, an amine-di-iso-propanol(ADIP) cooler, a regenerator overhead (OVHD) condenser, a Reid vaporpressure (RVP) column condenser, a depropanizer condenser, a debutanizercondenser, or combinations thereof. The product treating processes orsections can include the following non-limiting heat sources: a propanedehydrator condenser, a butane dehydrator condenser, a propanecondenser, an air-cooled condenser, a regeneration gas cooler, and abutane condenser, or combinations thereof. The natural gasolineprocessing processes or sections can include, but are not limited to, anatural gasoline (NG) flash vapor condenser, a NG decolorizer condenser,or combinations thereof.

Fractionation Section

Fractionation is the process of separating the different components ofnatural gas. Separation is possible because each component has adifferent boiling point. At temperatures less than the boiling point ofa particular component, that component condenses to a liquid. It is alsopossible to increase the boiling point of a component by increasing thepressure. By using columns operating at different pressures andtemperatures, the NGL fractionation plant is capable of separatingethane, propane, butane, pentane, or combinations thereof (with orwithout heavier associated hydrocarbons) from NGL fractionation feeds.Deethanizing separates ethane from C2+ NGL, where C2 refers to amolecule containing two carbon atoms (ethane), and where C2+ refers to amixture containing molecules having two or more carbon atoms, forexample, a NGL containing C2, C3, C4, C5 can be abbreviated as “C2+NGL.” Depropanizing and debutanizing separate propane and butane,respectively, from C3+ NGL and C4+ NGL, respectively. Because theboiling points of heavier natural gases are closer to each other, suchgases can be harder to separate compared to lighter natural gases. Also,a rate of separation of heavier components is less than that ofcomparatively lighter components. In some instances, the NGLfractionation plant can implement, for example, about 45 distillationtrays in the deethanizer, about 50 trays in the depropanizer, and about55 trays in the debutanizer.

The fractionation section can receive a feed gas containing C2+ NGL fromgas plants, which are upstream plants that condition and sweeten thefeed gas, and produce a sales gas, such as a C1/C2 mixture, where C1 isabout 90%, as a final product. The C2+ NGL from gas plants can befurther processed in the NGL fractionation plant for C2+ recovery. Fromfeed metering or surge unit metering (or both), feed flows to the threefractionation modules, namely, the deethanizing module, thedepropanizing module and the debutanizing module, each of which isdescribed later.

Deethanizer Module (or Deethanizer Column)

The C2+ NGL is pre-heated before entering the deethanizer column forfractionation. The separated ethane leaves the column as overhead gas.The ethane gas is condensed by a closed-loop propane refrigerationsystem. After being cooled and condensed, the ethane is a mixture of gasand liquid. The liquid ethane is separated and pumped back to the top ofthe column as reflux. The ethane gas is warmed in an economizer and thensent to users. The bottoms product from the deethanizer reboiler is C3+NGL, which is sent to the depropanizer module.

Depropanizer Module (or Depropanizer Column)

From the deethanizer module, C3+ NGL enters the depropanizer module forfractionation. The separated propane leaves the column as overhead gas.The gas is condensed using coolers. The propane condensate is collectedin a reflux drum. Some of the liquid propane is pumped back to thecolumn as reflux. The rest of the propane is either treated or sent tousers as untreated product. The bottoms product from the depropanizerreboiler, C4+ is then sent to the debutanizer module

Debutanizer Module (or Debutanizer Column)

C4+ enters the debutanizer module for fractionation. The separatedbutane leaves the column as overhead gas. The gas is condensed usingcoolers. The butane condensate is collected in a reflux drum. Some ofthe liquid butane is pumped back to the column as reflux. The rest ofthe butane is either treated or sent to users as untreated product. Thebottoms product from the debutanizer reboiler, C5+ natural gas (NG) goeson to a RVP control section (which may also be referred to as a rerununit), which will be discussed in greater detail in a later section.

Product Treating Section

While ethane requires no further treatment, propane and butane productsare normally treated to remove hydrogen sulfide (H₂S), carbonyl sulfide(COS), and mercaptan sulfur (RSH). Then, the products are dried toremove any water. All exported product is treated, while untreatedproducts can go to other industries. As described later, propanereceives ADIP treating, MEROX™ (Honeywell UOP; Des Plaines, Ill.)treating, and dehydration. Butane receives MEROX treating, anddehydration.

ADIP Treating Section

ADIP is a solution of di-isopropanol amine and water. ADIP treatingextracts H₂S and COS from propane. The ADIP solution, through contactwith the sour propane, absorbs the H₂S and COS. The ADIP solution firstcontacts the sour propane in an extractor. In the extractor, the ADIPabsorbs most of the H₂S and some of the COS. The propane then passesthrough a mixer/settler train where the propane contacts with ADIPsolution to extract more H₂S and COS. This partially sweetened propaneis cooled and then washed with water to recover the ADIP entrained withthe propane. The propane is then sent to MEROX treating, which isdescribed later. The rich ADIP that has absorbed the H₂S and COS leavesthe bottom of the extractor and is regenerated into lean ADIP for reuse.The regenerator column has a temperature and pressure that are suitablefor acid gas removal. When the rich ADIP enters the regenerator, theentrained acid gases are stripped. As the acid gases leaves theregenerator as overhead, any free water is removed to prevent acidformation. The acid gases are then sent to flare. The lean ADIP leavesthe extractor bottom and is cooled and filtered. Lean ADIP returns tothe last mixer/settler and flows back through the system in thecounter-current direction of the propane to improve contact between thepropane and ADIP, which improves H₂S and COS extraction.

C3/C4 MEROX Treating Section

MEROX treating removes mercaptan sulfur from C3/C4 product. Mercaptansare removed using a solution of sodium hydroxide (NaOH), also known bythe commercial name caustic soda (hereinafter referred to as “caustic”)and MEROX. The MEROX catalyst facilitates the oxidation of mercaptans todisulfides. The oxidation takes place in an alkaline environment, whichis provided by using the caustic solution. MEROX treating for C3 and C4is similar. Both products are prewashed with caustic to remove anyremaining traces of H₂S, COS, and CO₂. This prevents damage to thecaustic that is used in MEROX treating. After prewashing, product flowsto an extractor, where a caustic solution with MEROX catalyst contactswith the product. The caustic/catalyst solution converts the mercaptansinto mercaptides. The sweetened product, which is lean on acid gases,leaves the extractor as overhead and any remaining caustic is separated.Caustic leaves the bottom of both product extractors rich withmercaptides. The rich caustic is regenerated into lean caustic forreuse. The C3/C4 extraction sections share a common caustic regenerationsection, namely, an oxidizer. Before entering the bottom of theoxidizer, the rich caustic is injected with MEROX catalyst to maintainproper catalyst concentration, heated, and mixed with process air. Inthe oxidizer, the mercaptides are oxidized into disulfides. The mixtureof disulfides, caustic, and air leave the oxidizer as overhead. The air,disulfide gases, and disulfide oil are separated from the regeneratedcaustic. The regenerated caustic is pumped to the C3/C4 extractor.Regenerated caustic with any residual disulfides is washed with NG inthe NG wash settler.

C3/C4 Dehydration Section

Propane or butane products (or both) contain water when they leave MEROXtreating. Dehydration removes moisture in such products throughadsorption before the products flow to refrigeration and storage. Thedehydration processes for C3 and C4 are similar. Both C3/C4 dehydrationsections have two dehydrators containing molecular sieve desiccant beds.One dehydrator is in service while the other undergoes regeneration.Regeneration consists of heating the sieve beds to remove moisture, thencooling the beds before reuse. During drying, product flows up andthrough the molecular sieve bed, which adsorbs (that is, binds to itssurface) moisture. From the top of the dehydrator, dry C3/C4 productsflow to refrigeration.

Natural Gasoline (NG) Processing Section

NG processing includes RVP control, decolorizing and depentanizingsections.

RVP Control Section

A Reid vapor pressure (RVP) control section (or rerun unit) is afractionator column that receives the C5+ NG from the debutanizerbottom. The RVP control section collects a pentane product. The RVPcontrol section can be used to adjust the RVP of the pentane product ata rerun fractionator overhead before the pentane product is sent to apentane storage tank. RVP is a measure of the ability of a hydrocarbonto vaporize. RVP (sometimes called volatility) is an importantspecification in gasoline blending. The RVP control section stabilizesthe RVP of NG by removing small amounts of pentane. Depending onoperational requirements, the RVP control section can be totally orpartially bypassed. NG from the debutanizer bottoms goes to the RVPcolumn where a controlled amount of pentane is stripped and leaves thecolumn as overhead gas. As in NGL fractionation, the overhead gas iscondensed with coolers, and some of the condensate is pumped back to thecolumn as reflux. The remaining pentane is cooled and sent to storage.If the RVP column bottoms product (NG) meets color specifications, it issent to storage. If not, it is sent to decolorizing.

Decolorizing Section

The decolorizing section removes color bodies from NG. Color bodies aretraces of heavy ends found in the debutanizer bottoms product. Otherimpurities such as corrosion products from the pipeline may also bepresent. These must be removed for NG to meet the color specification.Decolorizer feed can be RVP column bottoms product or debutanizerbottoms product, or a combination of both. Additional natural gasolinecan also be supplied from other facilities to maintain a hexane plus(C6+) product supply. If decolorizing is needed, NG first passes througha pre-flash-drum. A large portion of the lighter NG components vaporizesand leaves the drum as overhead. The heavier NG components remain alongwith the color bodies and are fed to the decolorizer column, where theremaining color bodies are separated. The NG leaves the decolorizer asoverhead gas and is condensed and collected in the NG product drum, withsome pumped back to the column as reflux. Overhead from the column andflash drum are joined and pumped to either the depentanizer (describedlater) or cooled and sent to storage in the feed product surge unit. Thecolor bodies leave the decolorizer as bottoms product and are pumped tothe feed and surge unit to be injected into a crude line.

Depentanizing Section

Depentanizing uses a fractionation column to produce a pentane overheadproduct and a C6+ bottoms product. Both the pentane product and the C6+bottoms product are separately fed to storage or downstream thepetrochemical plants. The feed to the depentanizer is the NG productstream from the decolorizing section. Feed can be increased or decreasedbased on the demand for C6+ bottoms product. If the NGL fractionationplant NG production cannot meet demand, NG can be imported from oilrefineries. The decolorized NG is preheated before entering thedepentanizer. The separated pentane leaves the column as overhead gas.The overhead condensers cool the overhead stream, and some is pumpedback to the column as reflux. The remaining pentane is cooled and sentto storage. Light NG in the bottoms is vaporized and returned to heatthe depentanizer. The remaining bottoms product is cooled and sent tostorage as C6+.

Table 2 lists duty per train of major waste heat streams in an exampleof an NGL fractionation plant.

TABLE 2 Duty/train Stream Name (MMBtu/h) Propane refrigerant condenser94 Propane dehydration condenser 22 Butane dehydrator condenser 9Naphtha cooler 11 Depentanizer condenser 100 ADIP cooler 73 RegeneratorOVHD condenser 18 NG flash vapor condenser 107 NG decolorizer condenser53 Natural gasoline (cooling) process propane 29 condenser Fractionationpropane condenser 81 Air cooled condenser 16 Regeneration gas cooler 22RVP column condenser 36 Butane condenser 49 Depropanizer condenser 194Debutanizer condenser 115

In Table 2, “Duty/train” represents each stream's thermal duty inmillions Btu per hour (MMBtu/h) per processing train. A typical NGLfractionation plant includes three to four processing trains.

The systems described in this disclosure can be integrated with a NGLfractionation plant to make the fractionation plant more energyefficient or less polluting or both. In particular, the energyconversion system can be implemented to recover low grade waste heatfrom the NGL fractionation plant. Low grade waste heat is characterizedby a temperature difference between a source and sink of the low gradeheat steam being between 65° C. and 232° C. (150° F. and 450° F.). TheNGL fractionation plant is an attractive option for integration withenergy conversion systems due to a large amount of low grade waste heatgenerated by the plant and an absence of a need for deep cooling. Deepcooling refers to a temperature that is less than ambient that uses arefrigeration cycle to maintain.

The low grade waste heat from an NGL fractionation plant can be used forcommodities such as carbon-free power generation, cooling capacitygeneration, potable water production from sea water, or combinationsthereof. Low grade waste heat is characterized by a temperature rangingbetween 65° C. and 232° C. (150° F. to 450° F.). The waste heat can beused for the mono-generation, co-generation, or tri-generation of one ormore or all of the commodities mentioned earlier. Low grade waste heatfrom the NGL fractionation plant can be used to provide in-plantsub-ambient cooling, thus reducing the consumption of power or fuel (orboth) of the plant. Low grade waste heat from the NGL fractionationplant can be used to provide ambient air conditioning or cooling in theindustrial community or in a nearby non-industrial community, thushelping the community to consume energy from alternative sources. Inaddition, the low grade waste heat can be used to desalinate water andproduce potable water to the plant and adjacent community. An NGLfractionation plant is selected for low grade waste heat recoverybecause of a quantity of low grade waste heat available from the NGLfractionation plant as well as a cooling requirement of the plant toambient temperature cooling (instead of deep cooling).

The energy conversion systems described in this disclosure can beintegrated into an existing NGL fractionation plant as a retrofit or canbe part of a newly constructed NGL fractionation plant. A retrofit to anexisting NGL fractionation plant allows the carbon-free powergeneration, and fuel savings advantages offered by the energy conversionsystems described here to be accessible with a reduced capitalinvestment. For example, the energy conversion systems described herecan produce one or more or all of substantially between 35 MW and 40 MW(for example, 37 MW) of carbon-free power, substantially between 100,000and 150,000 m³/day (for example, 120,000 m³/day) of desalinated water,and substantially between 350 MM BTU/h and 400 MM BTU/h (for example,388 MM BTU/h) of cooling capacity for in-plant or community utilizationor both.

As described later, the systems for waste heat recovery and re-use fromthe NGL fractionation plant can include modified multi-effectdistillation (MED) systems, customized Organic Rankine Cycle (ORC)systems, unique ammonia-water mixture Kalina cycle systems, customizedmodified Goswami cycle systems, mono-refrigerant specific vaporcompression-ejector-expander triple cycle systems, or combinations ofone or more of them. Details of each disclosure are described in thefollowing paragraphs.

Heat Exchangers

In the configurations described in this disclosure, heat exchangers areused to transfer heat from one medium (for example, a stream flowingthrough a plant in a NGL fractionation plant, a buffer fluid or othermedium) to another medium (for example, a buffer fluid or differentstream flowing through a plant in the NGL fractionation plant). Heatexchangers are devices which transfer (exchange) heat typically from ahotter fluid stream to a relatively less hotter fluid stream. Heatexchangers can be used in heating and cooling applications, for example,in refrigerators, air conditions or such cooling applications. Heatexchangers can be distinguished from one another based on the directionin which fluids flow. For example, heat exchangers can be parallel-flow,cross-flow or counter-current. In parallel-flow heat exchangers, bothfluid involved move in the same direction, entering and exiting the heatexchanger side-by-side. In cross-flow heat exchangers, the fluid pathruns perpendicular to one another. In counter-current heat exchangers,the fluid paths flow in opposite directions, with one fluid exitingwhether the other fluid enters. Counter-current heat exchangers aresometimes more effective than the other types of heat exchangers.

In addition to classifying heat exchangers based on fluid direction,heat exchangers can also be classified based on their construction. Someheat exchangers are constructed of multiple tubes. Some heat exchangersinclude plates with room for fluid to flow in between. Some heatexchangers enable heat exchange from liquid to liquid, while some heatexchangers enable heat exchange using other media.

Heat exchangers in a NGL fractionation plant are often shell and tubetype heat exchangers which include multiple tubes through which fluidflows. The tubes are divided into two sets—the first set contains thefluid to be heated or cooled; the second set contains the fluidresponsible for triggering the heat exchange, in other words, the fluidthat either removes heat from the first set of tubes by absorbing andtransmitting the heat away or warms the first set by transmitting itsown heat to the fluid inside. When designing this type of exchanger,care must be taken in determining the correct tube wall thickness aswell as tube diameter, to allow optimum heat exchange. In terms of flow,shell and tube heat exchangers can assume any of three flow pathpatterns.

Heat exchangers in NGL facilities can also be plate and frame type heatexchangers. Plate heat exchangers include thin plates joined togetherwith a small amount of space in between, often maintained by a rubbergasket. The surface area is large, and the corners of each rectangularplate feature an opening through which fluid can flow between plates,extracting heat from the plates as it flows. The fluid channelsthemselves alternate hot and cold liquids, meaning that the heatexchangers can effectively cool as well as heat fluid. Because plateheat exchangers have large surface area, they can sometimes be moreeffective than shell and tube heat exchangers.

Other types of heat exchangers can include regenerative heat exchangersand adiabatic wheel heat exchangers. In a regenerative heat exchanger,the same fluid is passed along both sides of the exchanger, which can beeither a plate heat exchanger or a shell and tube heat exchanger.Because the fluid can get very hot, the exiting fluid is used to warmthe incoming fluid, maintaining a near constant temperature. Energy issaved in a regenerative heat exchanger because the process is cyclical,with almost all relative heat being transferred from the exiting fluidto the incoming fluid. To maintain a constant temperature, a smallquantity of extra energy is needed to raise and lower the overall fluidtemperature. In the adiabatic wheel heat exchanger, an intermediateliquid is used to store heat, which is then transferred to the oppositeside of the heat exchanger. An adiabatic wheel consists of a large wheelwith threads that rotate through the liquids—both hot and cold—toextract or transfer heat. The heat exchangers described in thisdisclosure can include any one of the heat exchangers described earlier,other heat exchangers, or combinations of them.

Each heat exchanger in each configuration can be associated with arespective thermal duty (or heat duty). The thermal duty of a heatexchanger can be defined as an amount of heat that can be transferred bythe heat exchanger from the hot stream to the cold stream. The amount ofheat can be calculated from the conditions and thermal properties ofboth the hot and cold streams. From the hot stream point of view, thethermal duty of the heat exchanger is the product of the hot stream flowrate, the hot stream specific heat, and a difference in temperaturebetween the hot stream inlet temperature to the heat exchanger and thehot stream outlet temperature from the heat exchanger. From the coldstream point of view, the thermal duty of the heat exchanger is theproduct of the cold stream flow rate, the cold stream specific heat anda difference in temperature between the cold stream outlet from the heatexchanger and the cold stream inlet temperature from the heat exchanger.In several applications, the two quantities can be considered equalassuming no heat loss to the environment for these units, particularly,where the units are well insulated. The thermal duty of a heat exchangercan be measured in watts (W), megawatts (MW), millions of BritishThermal Units per hour (Btu/hr.), or millions of kilocalories per hour(Kcal/h). In the configurations described here, the thermal duties ofthe heat exchangers are provided as being “about X MW,” where “X”represents a numerical thermal duty value. The numerical thermal dutyvalue is not absolute. That is, the actual thermal duty of a heatexchanger can be approximately equal to X, greater than X or less thanX.

Flow Control System

In each of the configurations described later, process streams (alsocalled “streams”) are flowed within each plant in a NGL fractionationplant and between plants in the NGL fractionation plant. The processstreams can be flowed using one or more flow control systems implementedthroughout the NGL fractionation plant. A flow control system caninclude one or more flow pumps to pump the process streams, one or moreflow pipes through which the process streams are flowed and one or morevalves to regulate the flow of streams through the pipes.

In some implementations, a flow control system can be operated manually.For example, an operator can set a flow rate for each pump and set valveopen or close positions to regulate the flow of the process streamsthrough the pipes in the flow control system. Once the operator has setthe flow rates and the valve open or close positions for all flowcontrol systems distributed across the NGL fractionation plant, the flowcontrol system can flow the streams within a plant or between plantsunder constant flow conditions, for example, constant volumetric rate orsuch flow conditions. To change the flow conditions, the operator canmanually operate the flow control system, for example, by changing thepump flow rate or the valve open or close position.

In some implementations, a flow control system can be operatedautomatically. For example, the flow control system can be connected toa computer system to operate the flow control system. The computersystem can include a computer-readable medium storing instructions (suchas flow control instructions and other instructions) executable by oneor more processors to perform operations (such as flow controloperations). An operator can set the flow rates and the valve open orclose positions for all flow control systems distributed across the NGLfractionation plant using the computer system. In such implementations,the operator can manually change the flow conditions by providing inputsthrough the computer system. Also, in such implementations, the computersystem can automatically (that is, without manual intervention) controlone or more of the flow control systems, for example, using feedbacksystems implemented in one or more plants and connected to the computersystem. For example, a sensor (such as a pressure sensor, temperaturesensor or other sensor) can be connected to a pipe through which aprocess stream flows. The sensor can monitor and provide a flowcondition (such as a pressure, temperature, or other flow condition) ofthe process stream to the computer system. In response to the flowcondition exceeding a threshold (such as a threshold pressure value, athreshold temperature value, or other threshold value), the computersystem can automatically perform operations. For example, if thepressure or temperature in the pipe exceeds the threshold pressure valueor the threshold temperature value, respectively, the computer systemcan provide a signal to the pump to decrease a flow rate, a signal toopen a valve to relieve the pressure, a signal to shut down processstream flow, or other signals.

FIGS. 1A-1O are schematic illustrations of a power generation systemthat utilizes waste heat from one or more heat sources in a natural gasliquid (NGL) fractionation plant.

FIG. 1A is a schematic diagram of an example system 300 to recover wasteheat from heat sources in an NGL fractionation plant. FIGS. 1B-1O areschematic diagrams illustrating the location of the heat sources withinthe NGL fractionation plant, as well as the interaction (for example,fluid and thermal) with existing components of the NGL fractionationplant. In this example system 300, there are seventeen heat sources inthe NGL fractionation plant. In this example system 300, the seventeenheat sources in the NGL fractionation plant are divided into two heatingfluid circuits that, in some portions of the two circuits, areseparated, and in other portions of the two circuits are combined. Inthis example system 300, one of the two heating fluid circuits servesonly a first power generation system, while both heating fluid circuitsserve a second power generation system.

Generally, the NGL fractionation plant contains a large amount of lowgrade waste heat. This waste heat can be used to produce water, cooling,power, or a combination of two or more. In some aspects, embodiments ofthe present disclosure include a system (such as system 300) thatrecovers the waste heat available in the NGL fractionation plant using aheat recovery network that includes multiple (for example, seventeen insome embodiments) heat exchangers distributed in particular areas of theNGL fractionation plant. In some embodiments, the system 300 cangenerate about 37 MW using dual organic Rankine cycle (ORC) systems. Thelow grade waste heat is recovered from processing units within the NGLfractionation using, for example, one or more buffer streams such as hotoil or pressurized water streams.

In example embodiments, the buffer streams flow from a storage tank atabout 113° F. and are directed towards specific units in the NGLfractionation plant to recover particular amounts of thermal energy, asshown in FIGS. 1B-1O. The thermal energy absorbed from the NGLfractionation plant increases the buffer streams original temperaturefrom about 113° F. to about 160° F. in a low temperature buffer streamand from about 113° F. to about 238° F. in a high temperature bufferstream. The buffer streams at 160° F. and 238° F. are then used as shownin FIG. 1A to produce about 37 MW using the dual ORC systems (describedlater). The buffer streams are reduced in temperature in the respectiveORC systems to about 113° F. and flow back to the storage tank, wherethey are recombined.

FIG. 1A is a schematic diagram of the example system 300 to recoverwaste heat from the seventeen heat sources in the NGL fractionationplant. In some implementations, the system 300 can include a firstheating fluid circuit 302 thermally coupled to a portion of the multipleheat sources. For example, the portion of multiple heat sources that arethermally coupled to the first heating fluid circuit 302 can includeseven of the seventeen heat exchangers, including a first heat exchanger302 a, a second heat exchanger 302 b, a third heat exchanger 302 c, afourth heat exchanger 302 d, a fifth heat exchanger 302 e, a sixth heatexchanger 302 f, and a seventh heat exchanger 302 g. In someimplementations, the seven heat sources can be connected in parallel(for example, relative to a flow of a buffer fluid). In someimplementations, a single heat exchanger shown in a figure mayillustrate one or more heat exchangers.

The system 300, as shown in FIG. 1A, can also include a second heatingfluid circuit 304 thermally coupled to another portion of the multipleheat sources. For example, the portion of multiple heat sources that arethermally coupled to the second heating fluid circuit 304 can includeten of the seventeen heat exchangers, including a first heat exchanger304 a, a second heat exchanger 304 b, a third heat exchanger 304 c, afourth heat exchanger 304 d, a fifth heat exchanger 304 e, a sixth heatexchanger 304 f, a seventh heat exchanger 304 g, an eighth heatexchanger 304 h, a ninth heat exchanger 304 i, and a tenth heatexchanger 304 j. In some implementations, the ten heat sources can beconnected in parallel (for example, relative to a flow of a bufferfluid). In some implementations, a single heat exchanger shown in afigure may illustrate one or more heat exchangers.

The example system 300 can include a first power generation system 314that includes a first organic Rankine cycle (ORC). The first ORC caninclude a working fluid 316 that is thermally coupled to the secondheating fluid circuit 304 to heat the working fluid 316. In someimplementations, the working fluid 316 can be isobutane. The first ORCcan also include a gas expander 320 configured to generate electricalpower from the heated working fluid 316. As shown in FIG. 1A, the firstORC can additionally include an evaporator 318, a pump 324 and acondenser 322. In some implementations, the working fluid 316 can bethermally coupled to the second heating fluid circuit 304 in theevaporator 316.

The example system 300 also includes a second power generation system326 that includes a second organic Rankine cycle (ORC). The second ORCcan include a working fluid 328 that is thermally coupled to the firstheating fluid circuit 302 and the second heating fluid circuit 304 toheat the working fluid 328. In some implementations, the working fluid328 can be isobutane. The second ORC can also include a gas expander 332configured to generate electrical power from the heated working fluid328. As shown in FIG. 1A, the second ORC can additionally include anevaporator 330, a pump 334 and the condenser 322. In someimplementations, the working fluid 328 can be thermally coupled to thefirst heating fluid circuit 302 and the second heating fluid circuit 304in the evaporator 330.

In operation, a first heating fluid 306 (for example, water, oil, orsuch fluid) is circulated through the seven heat exchangers of the firstheating fluid circuit 302. An inlet temperature of the first heatingfluid 306 that is circulated into the inlets of each of the seven heatsources is the same or substantially the same subject to any temperaturevariations that may result as the heating fluid 306 flows throughrespective inlets. Each heat exchanger heats the heating fluid 306 to arespective temperature that is greater than the inlet temperature. Theheated first heating fluid 306 from the seven heat exchangers arecombined and then combined with a second heating fluid 308 at an outletof the evaporator 318. The combined flows of the first and secondheating fluids 306 and 308 are flowed through the evaporator 330 of thesecond ORC. Heat from the heated heating fluids 306 and 308 heats theworking fluid 328 of the second ORC thereby increasing the working fluidtemperature and evaporating the working fluid 328. The heat exchangewith the working fluid 328 results in a decrease in the temperature ofthe combined flow of the first and second heating fluids 306 and 308.The combined flow of the first and second heating fluids 306 and 308 isthen collected in a heating fluid tank 310 and can be pumped, by a pump312, back through the seventeen heat exchangers of the first and secondheating fluid circuits 302 and 304 to restart the waste heat recoverycycle.

In further operations, the second heating fluid 308 (for example, afluid similar to or identical to the first heating fluid 306) iscirculated through the ten heat exchangers of the second heating fluidcircuit 304. An inlet temperature of the second heating fluid 308 thatis circulated into the inlets of each of the ten heat sources is thesame or substantially the same subject to any temperature variationsthat may result as the heating fluid 308 flows through respectiveinlets. Each heat exchanger heats the second heating fluid 308 to arespective temperature that is greater than the inlet temperature. Theheated second heating fluid 308 from the ten heat exchangers is flowedthrough the evaporator 318 of the first ORC. The second heating fluid308 then combines with the first heating fluid 306, as describedpreviously, to heat the second working fluid 328 in the evaporator 330.Heat from the heated second heating fluid 308 heats the working fluids316 and 328 of the first and second ORCs, thereby increasing the workingfluid temperatures and evaporating the working fluids 316 and 328. Theheat exchange with the working fluids 316 and 328 results in a decreasein the temperature of the second heating fluid 308. The combined flow ofthe first and second heating fluids 306 and 308 is then collected in aheating fluid tank 310 and can be pumped, by a pump 312, back throughthe seventeen heat exchangers of the first and second heating fluidcircuits 302 and 304 to restart the waste heat recovery cycle. Asillustrated, the heating fluids 306 and 308 are separated downstream ofthe pump 312.

The heating fluid circuits 302 and 304 to flow heating fluids 306 and308 through the seventeen heat exchangers can include multiple valvesthat can be operated manually or automatically. For example, the NGLfractionation plant can be fitted with the heating fluid flow pipes andvalves. An operator can manually open each valve in the circuit to causethe heating fluids 306 and 308 to flow through the circuits 302 and 304,respectively. To cease waste heat recovery, for example, to performrepair or maintenance or for other reasons, the operator can manuallyclose each valve in the circuits 302 and 304. Alternatively, a controlsystem, for example, a computer-controlled control system, can beconnected to each valve in the circuits 302 and 304. The control systemcan automatically control the valves based, for example, on feedbackfrom sensors (for example, temperature, pressure or such sensors),installed at different locations in the circuits 302 and 304. Thecontrol system can also be operated by an operator.

In the manner described earlier, the heating fluids 306 and 308 can belooped through the seventeen heat exchangers to recover heat that wouldotherwise go to waste in the NGL fractionation plant, and to use therecovered waste heat to operate the power generation systems 314 and326. By doing so, an amount of energy needed to operate the powergeneration systems 314 and 326 can be decreased while obtaining the sameor substantially similar power output from the power generation systems314 and 326. For example, the power output from the power generationsystems 314 and 326 that implements the waste heat recovery network canbe higher or lower than the power output from a power generation systemthat does not implement the waste heat recovery network. Where the poweroutput is less, the difference may not be statistically significant.Consequently, a power generation efficiency of the NGL fractionationplant can be increased.

FIG. 1A illustrates an example dual-ORC power generation system 300 thatuses, for example, iso-butane as the working fluid 316 at a highpressure of about 15 to 17 bar and as the working fluid 328 at a lowpressure of about 6 to 8 bar to generate about 37 MW of power. Theheating fluid 308 (for example, hot oil or water) at about 240° F. fromthe second heating fluid circuit 304 in the NGL fractionation plant isused in a high pressure cycle (power generation system 314) to preheatand vaporize the high pressure working fluid 316 that flows to the gasexpander 320 to generate about 17 MW of power. The ten heat exchangersof the second heating fluid circuit 304 have about 650 MM BTU/h ofthermal load of waste heat recovered from the heating fluid 308 thatcollects this thermal energy from specific units in the NGLfractionation plant. This heating fluid 308 at about 240° F. is cooleddown in the evaporator 318 of the power generation system 314 to about160° F. At this temperature, the heating fluid 308 joins the heatingfluid 306 of the first heating fluid circuit 302.

The combined heating fluids 306 and 308, at about 160° F. is used in theevaporator 330 to preheat and vaporize the low pressure working fluid328 that flows to the gas expander 332 to generate about 20 MW of power.The seventeen heat exchangers of the first and second heating fluidcircuits 302 and 304 have about 2350 MM BTU/h of waste heat recoveredfrom specific units in the NGL fractionation plant.

The second heating fluid 308 at a temperature of about 240° F. is usedto preheat and vaporize the high pressure working fluid 316 that flowsto the gas expander 320 to generate about 17 MW of power. Thesuperheated vapor of the working fluid 316 leaving the gas expander 320is then combined with the vapor of the working fluid 328 exiting the gasexpander 332 and both are condensed using the condenser 322 (forexample, with water as a cooling medium at 77° F.). The condensedworking fluids 316 and 328 are then pumped back to the two cycleoperating pressures using respective pumps 324 and 334, and the cyclescontinue in evaporators 318 and 330.

FIG. 1B shows the first heat exchanger 302 a in a deethanizer section ofthe NGL fractionation plant. In this example, the heat exchanger 302 ais positioned and thermally coupled to a heat source to recover wasteheat from the refrigeration compressor(s) of the deethanizer refluxgeneration unit(s). The heating fluid 306 is circulated from the tank310 at 113° F. to heat exchanger 302 a to cool down the outlet stream ofthe deethanizer refrigeration compressor. The heating fluid 306 isheated in the heat exchanger 302 a to between about 177° F. and 187° F.,for example, about 182° F. before it flows to a collection header tojoin other heating fluid streams 306 from other parts of the NGLfractionation plant to flow to the evaporator 330 of the powergeneration system 326. The total thermal duty of the heat exchanger 302a is about 479 MM BTU/H.

FIG. 1C shows the first heat exchanger 304 a in a propane dehydratorsection of the NGL fractionation plant. In this example, the heatexchanger 304 a is positioned and thermally coupled to a heat source torecover waste heat from the propane dehydration section. The heatingfluid 308 is circulated from the storage tank 310 at 113° F. to heatexchanger 304 a to cool down the outlet stream of the propanedehydrator. The heating fluid 308 is heated in the heat exchanger 304 ato between about 390° F. and 400° F., for example, about 395° F. beforeit is circulated to the collection header to join other heating fluidstreams 308 from other parts of the NGL fractionation plant to flow tothe evaporator 318 of the power generation system 314. The total thermalduty of the heat exchanger 304 a is about 96 MM BTU/H.

FIG. 1D shows the second heat exchanger 302 b in a depropanizer sectionof the NGL fractionation plant. In this example, the heat exchanger 302b is positioned and thermally coupled to a heat source to recover wasteheat from the depropanizer section. The heating fluid 306 is circulatedfrom the storage tank 310 at 113° F. to heat exchanger 302 b to cooldown the outlet stream of the depropanizer overhead stream. The heatingfluid 306 is heated in the heat exchanger 302 b to between about 129° F.and 139° F., for example, about 134° F. before it is circulated to thecollection header to join other heating fluid streams 306 from otherparts of the NGL fractionation plant to flow to the evaporator 330 ofthe power generation system 326. The total thermal duty of the heatexchanger 302 b is about 951 MM BTU/H.

FIG. 1E shows the second heat exchanger 304 b in a butane dehydratorsection of the NGL fractionation plant. In this example, the heatexchanger 304 b is positioned and thermally coupled to a heat source torecover waste heat from the butane dehydration section. The heatingfluid 304 is circulated from the storage tank 310 at 113° F. to heatexchanger 304 b to cool down the outlet stream of the butane dehydrator.The heating fluid 308 is heated in the heat exchanger 304 b to betweenabout 390° F. and 400° F., for example, about 395° F. before it iscirculated to the collection header to join other heating fluid streams308 from other parts of the NGL fractionation plant to flow to theevaporator 318 of the power generation system 314. The total thermalduty of the heat exchanger 302 b is about 47 MM BTU/H.

FIG. 1F shows the third heat exchanger 302 c and the third heatexchanger 304 c in a debutanizer section of the NGL fractionation plant.In this example, the heat exchangers 302 c and 304 c are positioned andthermally coupled to respective heat sources to recover waste heat fromthe debutanizer section. The heating fluid 306 is circulated from thestorage tank 310 at 113° F. to heat exchanger 302 c to cool down theoutlet stream of the debutanizer overhead stream. The heating fluid 306is heated in the heat exchanger 302 c to between about 147° F. and 157°F., for example, about 152° F. before it is circulated to the collectionheader to join other heating fluid streams 306 from other parts of theNGL fractionation plant then directed to flow to the evaporator 330 ofthe power generation system 326. The total thermal duty of the heatexchanger 302 c is about 587 MM BTU/H.

The heating fluid 308 is circulated from the storage tank 310 at 113° F.to heat exchanger 304 c to cool down the outlet stream of thedebutanizer bottoms. The heating fluid 308 is heated in the heatexchanger 304 c to between about 256° F. and 266° F., for example, about261° F. before it is circulated to the collection header to join theother heating fluid streams 308 from other parts of the NGLfractionation plant then directed to flow to the evaporator 318 of thepower generation system 314. The total thermal duty of the heatexchanger 304 c is about 56 MM BTU/H.

FIG. 1G shows the fourth heat exchanger 302 d in a depentanizer sectionof the NGL fractionation plant. In this example, the heat exchanger 302d is positioned and thermally coupled to a heat source to recover wasteheat from the depentanizer section. The heating fluid 306 is circulatedfrom the storage tank 310 at 113° F. to heat exchanger 302 d to cooldown the outlet stream of the depentanizer overhead stream. The heatingfluid 306 is heated in the heat exchanger 302 d to between about 160° F.and 170° F., for example, about 165° F. before it is circulated to thecollection header to join other heating fluid streams 306 from otherparts of the NGL fractionation plant then directed to flow to theevaporator 330 of the power generation system 326. The total thermalduty of the heat exchanger 302 d is about 100 MM BTU/H.

FIG. 1H shows the fourth heat exchanger 304 d and the fifth heatexchanger 304 e in a solvent regeneration section of the NGLfractionation plant. In this example, the heat exchangers 304 d and 304e are positioned and thermally coupled to respective heat sources torecover waste heat from the ADIP regeneration section. The heating fluid308 is circulated from the storage tank 310 at 113° F. to heat exchanger304 d to cool down the outlet stream of the ADIP regeneration sectionoverhead stream. The heating fluid 308 is heated in the heat exchanger304 d to between about 222° F. and 232° F., for example, about 227° F.before it is circulated to the collection header to join other heatingfluid streams 308 from other parts of the NGL fractionation plant thendirected to flow to the evaporator 318 of the power generation system314. The total thermal duty of the heat exchanger 304 d is about 18 MMBTU/H.

Another branch of the heating fluid 308 is circulated from the storagetank 310 at 113° F., to heat exchanger 302 i to cool down the outletstream of the ADIP regeneration section bottoms. The heating fluid 308is heated in the heat exchanger 304 e to between about 166° F. and 176°F., for example, about 171° F. before it is circulated to the collectionheader to join the other heating fluid streams 308 from other parts ofthe NGL fractionation plant then directed to flow to the evaporator 318of the power generation system 314. The total thermal duty of the heatexchanger 304 e is about 219 MM BTU/H.

FIG. 1I shows the fifth heat exchanger 302 e and the sixth heatexchanger 304 f in a natural gasoline decolorizing section of the NGLfractionation plant. In this example, the heat exchangers 302 e and 304f are positioned and thermally coupled to respective heat sources torecover waste heat from the natural gasoline decolorizing section. Theheating fluid 306 is circulated from the storage tank 310 at 113° F. toheat exchanger 302 e to cool down the outlet stream of the naturalgasoline decolorizing section pre-flash drum overhead stream. Theheating fluid 306 is heated in the heat exchanger 302 e to between about206° F. and 216° F., for example, about 211° F. before it is circulatedto the collection header to join other heating fluid streams 306 fromother parts of the NGL fractionation plant then directed to flow to theevaporator 330 of the power generation system 326. The total thermalduty of the heat exchanger 302 e is about 107 MM BTU/H.

The heating fluid 308 is circulated from the storage tank 310 at 113° F.to heat exchanger 304 f to cool down the outlet stream of the naturalgasoline decolorizer overhead stream. The heating fluid 308 is heated inthe heat exchanger 304 f to between about 224° F. and 234° F., forexample, about 229° F. before it is circulated to the collection headerto join the other heating fluid streams 308 from other parts of the NGLfractionation plant then directed to flow to the evaporator 318 of thepower generation system 314. The total thermal duty of the heatexchanger 304 f is about 53 MM BTU/H.

FIG. 1J shows the seventh heat exchanger 304 g in a propane tankrecovery section of the NGL fractionation plant. In this example, theheat exchanger 304 g is positioned and thermally coupled to a heatsource to recover waste heat from the propane tank vapor recoverysection. The heating fluid 308 is circulated from the storage tank 310at 113° F. to heat exchanger 304 g to cool down the outlet stream of thepropane vapor recovery compressor stream. The heating fluid 308 isheated in the heat exchanger 304 g to between about 258° F. and 268° F.,for example, about 263° F. before it is circulated to the collectionheader to join other heating fluid streams 308 from other parts of theNGL fractionation plant then directed to flow to the evaporator 318 ofthe power generation system 314. The total thermal duty of the heatexchanger 304 g is about 29 MM BTU/H.

FIG. 1K shows the sixth heat exchanger 302 f in a propane productrefrigeration section of the NGL fractionation plant. In this example,the heat exchanger 302 f is positioned and thermally coupled to a heatsource to recover waste heat from the propane product refrigerationsection. The heating fluid 306 is circulated from the storage tank 310at 113° F. to heat exchanger 302 f to cool down the outlet stream of thepropane refrigeration compressor stream. The heating fluid 306 is heatedin the heat exchanger 302 f to between about 187° F. and 197° F., forexample, about 192° F. before it is circulated to the collection headerto join other heating fluid streams 306 from other parts of the NGLfractionation plant then directed to flow to the evaporator 318 of thepower generation system 326. The total thermal duty of the heatexchanger 302 f is about 81 MM BTU/H.

FIG. 1L shows the eighth heat exchanger 304 h in a propane productsub-cooling section of the NGL fractionation plant. In this example, theheat exchanger 304 h is positioned and thermally coupled to a heatsource to recover waste heat from the propane product sub-coolingsection. The heating fluid 308 is circulated from the storage tank 310at 113° F. to heat exchanger 304 h to cool down the outlet stream of thepropane main compressor stream. The heating fluid 308 is heated tobetween about 232° F. and 242° F., for example, about 237° F. before itis circulated to the collection header to join other heating fluidstreams 308 from other parts of the NGL fractionation plant thendirected to flow to the evaporator 318 of the power generation system314. The total thermal duty of the heat exchanger 304 h is about 65 MMBTU/H.

FIG. 1M shows the seventh heat exchanger 302 g in a butane productrefrigeration section of the NGL fractionation plant. In this example,the heat exchanger 302 g is positioned and thermally coupled to a heatsource to recover waste heat from the butane product refrigerationsection. The heating fluid 306 is circulated from the storage tank 310at 113° F. to heat exchanger 302 g to cool down the outlet stream of thebutane refrigeration compressor stream. The heating fluid 306 is heatedin the heat exchanger 302 g to between about 142° F. and 152° F., forexample, about 147° F. before it is circulated to the collection headerto join other heating fluid streams 306 from other parts of the NGLfractionation plant then directed to flow to the evaporator 330 of thepower generation system 326. The total thermal duty of the heatexchanger 302 g is about 49 MM BTU/H.

FIG. 1N shows the ninth heat exchanger 304 i in an ethane productionsection of the NGL fractionation plant. In this example, the heatexchanger 304 i is positioned and thermally coupled to a heat source torecover waste heat from the ethane production section. The heating fluid308 is circulated from the storage tank 310 at 113° F. to heat exchanger304 i to cool down the outlet stream of the ethane dryer during thegeneration mode. The heating fluid 308 is heated in the heat exchanger304 i to between about 405° F. and 415° F., for example, about 410° F.before it is circulated to the collection header to join other heatingfluid streams 308 from other parts of the NGL fractionation plant thendirected to flow to the evaporator 318 of the power generation system314. The total thermal duty of the heat exchanger 304 i is about 22 MMBTU/H.

FIG. 1O shows the tenth heat exchanger 304 j in a natural gasoline vaporsection of the NGL fractionation plant. In this example, the heatexchanger 304 j is positioned and thermally coupled to a heat source torecover waste heat from the natural gasoline vapor pressure controlsection. The heating fluid 308 is circulated from the storage tank 310at 113° F. to heat exchanger 304 j to cool down the outlet stream of theReid vapor pressure control column overhead stream. The heating fluid308 is heated in the heat exchanger 304 j to between about 206° F. and216° F., for example, about 211° F. before it is circulated to thecollection header to join other heating fluid streams 308 from otherparts of the NGL fractionation plant then directed to flow to theevaporator 318 of the power generation system 314. The total thermalduty of the heat exchanger 304 j is about 36 MM BTU/H.

FIGS. 1A-1O illustrate schematic views of an example system 300 for apower conversion network that includes waste heat sources associatedwith a NGL fractionation plant. In this example system 300, a mini-powerplant synthesis uses two heating circuits of power generation systems314 and 326, sharing hot water (or other heating fluid) and isobutanesystems infrastructure, to generate power from specific portions of NGLfractionation plant low-low grade waste heat sources. In some aspects,the system 300 can be implemented in one or more steps, where each phasecan be separately implemented without hindering future steps toimplement the system 300. In some aspects, a minimum approachtemperature across a heat exchanger used to transfer heat from a heatsource to a working fluid (for example, water) can be as low as 3° C. ormay be higher. Higher minimum approach temperatures can be used in thebeginning of the phases at the expense of less waste heat recovery andpower generation, while reasonable power generation economics of scaledesigns are still attractive in the level of tens of megawatts of powergeneration.

In some aspects of system 300, optimized efficiency is realized uponusing a minimum approach temperature recommended for the specific heatsource streams used in the system design. In such example situations,optimized power generation can be realized without re-changing theinitial topology or the sub-set of low grade waste heat streamsselected/utilized from the NGL fractionation plant utilized in aninitial phase. System 300 and its related process scheme can beimplemented for safety and operability through dual ORC systems usingbuffer streams such as hot oil or high pressure hot water systems or amix of specified connections among buffer systems. The low-low gradewaste-heat-to-power-conversion (for example, less than the low gradewaste heat temperature defined by U.S. Department of Energy DOE as 232°C.) may be implemented using the dual ORC systems using isobutane as anorganic fluid at specific operating conditions.

The techniques to recover heat energy generated by the NGL fractionationplant described previously can be implemented in at least one or both oftwo example scenarios. In the first scenario, the techniques can beimplemented in an NGL fractionation plant that is to be constructed. Forexample, a geographic layout to arrange multiple sub-units of an NGLfractionation plant can be identified. The geographic layout can includemultiple sub-unit locations at which respective sub-units are to bepositioned. Identifying the geographic layout can include activelydetermining or calculating the location of each sub-unit in the NGLfractionation plant based on particular technical data, for example, aflow of petrochemicals through the sub-units starting from raw naturalgas or crude petroleum and resulting in refined natural gas. Identifyingthe geographic layout can alternatively or in addition include selectinga layout from among multiple previously-generated geographic layouts. Afirst subset of sub-units of the petrochemical refining system can beidentified. The first subset can include at least two (or more than two)heat-generating sub-units from which heat energy is recoverable togenerate electrical power. In the geographic layout, a second subset ofthe multiple sub-unit locations can be identified. The second subsetincludes at least two sub-unit locations at which the respectivesub-units in the first subset are to be positioned.

A first power generation system to recover heat energy from thesub-units in the first subset is identified. The first power generationsystem can be substantially similar to the first power generation systemdescribed earlier. In the geographic layout, a first power generationsystem location can be identified to position the first power generationsystem. At the identified first power generation system location, a heatenergy recovery efficiency is greater than a heat energy recoveryefficiency at other locations in the geographic layout.

A second power generation system to recover heat energy from thesub-units in the second subset is identified. The second powergeneration system can be substantially similar to the second powergeneration system described earlier. In the geographic layout, a secondpower generation system location can be identified to position thesecond power generation system. At the identified second powergeneration system location, a heat energy recovery efficiency is greaterthan a heat energy recovery efficiency at other locations in thegeographic layout.

The NGL fractionation plant planners and constructors can performmodeling or computer-based simulation experiments, or both, to identifyan optimal location for the power generation system to maximize heatenergy recovery efficiency, for example, by minimizing heat loss whentransmitting recovered heat energy from the at least two heat-generatingsub-units to the power generation system. The NGL fractionation plantcan be constructed according to the geographic layout by positioning themultiple sub-units at the multiple sub-unit locations, positioning thepower generation system at the power generation system location,interconnecting the multiple sub-units with each other such that theinterconnected multiple sub-units are configured to refine natural gasor crude oil, interconnecting the first power generation system with thesub-units in the first subset such that the first power generationsystem is configured to recover heat energy from the sub-units in thefirst subset and to provide the recovered heat energy to the first powergeneration system, and interconnecting the second power generationsystem with the sub-units in the second subset such that the secondpower generation system is configured to recover heat energy from thesub-units in the second subset and to provide the recovered heat energyto the second power generation system. The power generation systems areconfigured to generate power using the recovered heat energy.

In the second scenario, the techniques can be implemented in anoperational NGL fractionation plant. In other words, the powergeneration systems described earlier can be retrofitted to an alreadyconstructed and operational NGL fractionation plant.

The economics of industrial production, the limitations of global energysupply, and the realities of environmental conservation are concerns forall industries. It is believed that the world's environment has beennegatively affected by global warming caused, in part, by the release ofGHG into the atmosphere. Implementations of the subject matter describedhere can alleviate some of these concerns, and, in some cases, preventcertain NGL fractionation plants, which are having difficulty inreducing their GHG emissions, from having to shut down. By implementingthe techniques described here, specific portions in an NGL fractionationplant or an NGL fractionation plant, as a whole, can be made moreefficient and less polluting by carbon-free power generation fromspecific portions of low grade waste heat sources.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the claimsprovided in this document.

What is claimed is:
 1. A system, comprising: a first heating fluidcircuit thermally coupled to a first plurality of heat sources of anatural gas liquid (NGL) fractionation plant, the first plurality ofheat sources comprising: a first portion of first sub-units of the NGLfractionation plant that comprises an ethane system, a second pluralityof first sub-units of the NGL fractionation plant that comprises apropane system, a third portion of first sub-units of the NGLfractionation plant that comprises a butane system, a fourth portion offirst sub-units of the NGL fractionation plant that comprises a naturalgasoline system, and a fifth portion of first sub-units of the NGLfractionation plant that comprises a solvent regeneration system; asecond heating fluid circuit thermally coupled to a second plurality ofheat sources of the NGL fractionation plant, the second plurality ofheat sources comprising: a first portion of second sub-units of the NGLfractionation plant that comprises the ethane system, a second pluralityof second sub-units of the NGL fractionation plant that comprises thepropane system, a third portion of second sub-units of the NGLfractionation plant that comprises the butane system, a fourth portionof second sub-units of the NGL fractionation plant that comprises apentane system, and a fifth portion of second sub-units of the NGLfractionation plant that comprises the natural gasoline system; a firstpower generation system that comprises a first organic Rankine cycle(ORC), the first ORC comprising (i) a first portion of a working fluidthat is thermally coupled to the first heating fluid circuit in anevaporator of the first ORC to heat the first portion of the workingfluid, and (ii) a first expander configured to generate electrical powerfrom the heated first portion of the working fluid; a second powergeneration system that comprises a second organic Rankine cycle (ORC),the second ORC comprising (i) a second portion of the working fluid thatis thermally coupled to the first and second heating fluid circuits inan evaporator of the second ORC to heat the second portion of theworking fluid, and (ii) a second expander configured to generateelectrical power from the heated second portion of the working fluid;and a flow control system that comprises a first set of control valvesto selectively thermally couple a heating fluid of the first heatingfluid circuit to at least a portion of the first plurality of heatsources of the NGL fractionation plant, the control system furthercomprising a second set of control valves to selectively thermallycouple a heating fluid of the second heating fluid circuit to at least aportion of the second plurality of heat sources of the NGL fractionationplant.
 2. The system of claim 1, further comprising a heating fluid tankthat is fluidly coupled to the evaporators of the first and second ORCs.3. The system of claim 1, wherein the system further comprises conduitscontaining the working fluid and the working fluid comprises isobutane.4. The system of claim 3, the first and second fluid heating circuitsfurther comprise pipes containing water or oil.
 5. The system of claim4, further comprising: a condenser fluidly coupled to the first andsecond expanders and to a condenser fluid source to cool the workingfluid; a first pump to circulate the first portion of the working fluidthrough the first ORC; and a second pump to circulate the second portionof the working fluid through the second ORC.
 6. The system of claim 1,wherein the first and second fluid heating circuits further comprisepipes containing water or oil.
 7. The system of claim 1, furthercomprising: a condenser fluidly coupled to the first and secondexpanders and to a condenser fluid source to cool the working fluid; afirst pump to circulate the first portion of the working fluid throughthe first ORC; and a second pump to circulate the second portion of theworking fluid through the second ORC.
 8. The system of claim 1, whereinthe first portion of first sub-units of the NGL fractionation plantcomprises at least one ethane system heat source, comprising: a firstethane system heat source that comprises a heat exchanger that isthermally coupled to an outlet stream of an ethane dryer.
 9. The systemof claim 1, wherein the second portion of first sub-units of the NGLfractionation plant comprises at least three propane system heatsources, comprising: a first propane system heat source that comprises aheat exchanger that is thermally coupled to an outlet stream of apropane dehydrator; a second propane system heat source that comprises aheat exchanger that is thermally coupled to an outlet stream of apropane vapor recovery compressor stream; a third propane system heatsource that comprises a heat exchanger that is thermally coupled to anoutlet stream of a propane main compressor stream.
 10. The system ofclaim 1, wherein the third portion of first sub-units of the NGLfractionation plant comprises at least two butane system heat sources,comprising: a first butane system heat source that comprises a heatexchanger that is thermally coupled to an outlet stream of a butanedehydrator; and a second butane system heat source that comprises a heatexchanger that is thermally coupled to an outlet stream of a debutanizerbottoms.
 11. The system of claim 1, wherein the fourth portion of firstsub-units of the NGL fractionation plant comprises at least two naturalgasoline system heat sources, comprising: a first natural gasolinesystem heat source that comprises a heat exchanger that is thermallycoupled to an outlet stream of a natural gasoline decolorizer overheadstream; and a second natural gasoline system heat source that comprisesa heat exchanger that is thermally coupled to an outlet stream of a Reidvapor pressure control column overhead stream.
 12. The system of claim1, wherein the fifth portion of first sub-units of the NGL fractionationplant comprises at least two solvent regeneration system heat sources,comprising: a first solvent regeneration system heat source thatcomprises a heat exchanger that is thermally coupled to an outlet streamof an ADIP regeneration section overhead stream; and a second solventregeneration system heat source that comprises a heat exchanger that isthermally coupled to an outlet stream of an ADIP regeneration sectionbottoms.
 13. The system of claim 1, wherein the first portion of secondsub-units of the NGL fractionation plant comprises at least one ethanesystem heat source, comprising: a first ethane system heat source thatcomprises a heat exchanger that is thermally coupled to an outlet streamof a deethanizer refrigeration compressor.
 14. The system of claim 1,wherein the second portion of second sub-units of the NGL fractionationplant comprises at least two propane system heat sources, comprising: afirst propane system heat source that comprises a heat exchanger that isthermally coupled to an outlet stream of a depropanizer overhead stream;a second propane system heat source that comprises a heat exchanger thatis thermally coupled to an outlet stream of a propane refrigerationcompressor stream.
 15. The system of claim 1, wherein the third portionof second sub-units of the NGL fractionation plant comprises at leasttwo butane system heat sources, comprising: a first butane system heatsource that comprises a heat exchanger that is thermally coupled to anoutlet stream of a debutanizer overhead stream; and a second butanesystem heat source that comprises a heat exchanger that is thermallycoupled to an outlet stream of a butane refrigeration compressor stream.16. The system of claim 1, wherein the fourth portion of secondsub-units of the NGL fractionation plant comprises at least one pentanesystem heat source, comprising: a first pentane system heat source thatcomprises a heat exchanger that is thermally coupled to an outlet streamof a depentanizer overhead stream.
 17. The system of claim 1, whereinthe fifth portion of second sub-units of the NGL fractionation plantcomprises at least one natural gasoline system heat source, comprising:a first natural gasoline system heat source that comprises a heatexchanger that is thermally coupled to an outlet stream of a naturalgasoline decolorizing section pre-flash drum overhead stream.
 18. Amethod of recovering heat energy generated by a natural gas liquid (NGL)fractionation plant, the method comprising: circulating a first heatingfluid through a first heating fluid circuit thermally coupled to a firstplurality of heat sources of a natural gas liquid (NGL) fractionationplant, the first plurality of heat sources comprising: a first portionof first sub-units of the NGL fractionation plant that comprises anethane system, a second plurality of first sub-units of the NGLfractionation plant that comprises a propane system, a third portion offirst sub-units of the NGL fractionation plant that comprises a butanesystem, a fourth portion of first sub-units of the NGL fractionationplant that comprises a natural gasoline system, and a fifth portion offirst sub-units of the NGL fractionation plant that comprises a solventregeneration system; circulating a second heating fluid through a secondheating fluid circuit thermally coupled to a second plurality of heatsources of the NGL fractionation plant, the second plurality of heatsources comprising: a first portion of second sub-units of the NGLfractionation plant that comprises the ethane system, a second pluralityof second sub-units of the NGL fractionation plant that comprises thepropane system, a third portion of second sub-units of the NGLfractionation plant that comprises the butane system, a fourth portionof second sub-units of the NGL fractionation plant that comprises apentane system, and a fifth portion of second sub-units of the NGLfractionation plant that comprises the natural gasoline system;generating electrical power through a first power generation system thatcomprises a first organic Rankine cycle (ORC), the first ORC comprising(i) a first portion of a working fluid that is thermally coupled to thefirst heating fluid circuit in an evaporator of the first ORC to heatthe first portion of the working fluid, and (ii) a first expanderconfigured to generate electrical power from the heated first portion ofthe working fluid; generating electrical power through a second powergeneration system that comprises a second organic Rankine cycle (ORC),the second ORC comprising (i) a second portion of the working fluid thatis thermally coupled to the first and second heating fluid circuits inan evaporator of the second ORC to heat the second portion of theworking fluid, and (ii) a second expander configured to generateelectrical power from the heated second portion of the working fluid;actuating, with a flow control system, a first set of control valves toselectively thermally couple a heating fluid of the first heating fluidcircuit to at least a portion of the first plurality of heat sources ofthe NGL fractionation plant; and actuating, with the flow controlsystem, a second set of control valves to selectively thermally couple aheating fluid of the second heating fluid circuit to at least a portionof the second plurality of heat sources of the NGL fractionation plant.19. The method of claim 18, further comprising circulating the first andsecond heating fluids to a heating fluid tank from the evaporators ofthe first and second ORCs.
 20. The method of claim 19, wherein theworking fluid comprises isobutane.
 21. The method of claim 20, whereineach of the first and second heating fluids comprises water or oil. 22.The method of claim 21, further comprising: a condenser fluidly coupledto the first and second expanders and to a condenser fluid source tocool the working fluid; a first pump to circulate the first portion ofthe working fluid through the first ORC; and a second pump to circulatethe second portion of the working fluid through the second ORC.
 23. Themethod of claim 18, wherein the working fluid comprises isobutane. 24.The method of claim 18, wherein each of the first and second heatingfluids comprises water or oil.
 25. The method of claim 18, furthercomprising: a condenser fluidly coupled to the first and secondexpanders and to a condenser fluid source to cool the working fluid; afirst pump to circulate the first portion of the working fluid throughthe first ORC; and a second pump to circulate the second portion of theworking fluid through the second ORC.
 26. The method of claim 18,wherein the first portion of first sub-units of the NGL fractionationplant comprises at least one ethane system heat source, comprising: afirst ethane system heat source that comprises a heat exchanger that isthermally coupled to an outlet stream of an ethane dryer.
 27. The methodof claim 18, wherein the second portion of first sub-units of the NGLfractionation plant comprises at least three propane system heatsources, comprising: a first propane system heat source that comprises aheat exchanger that is thermally coupled to an outlet stream of apropane dehydrator; a second propane system heat source that comprises aheat exchanger that is thermally coupled to an outlet stream of apropane vapor recovery compressor stream; a third propane system heatsource that comprises a heat exchanger that is thermally coupled to anoutlet stream of a propane main compressor stream.
 28. The method ofclaim 18, wherein the third portion of first sub-units of the NGLfractionation plant comprises at least two butane system heat sources,comprising: a first butane system heat source that comprises a heatexchanger that is thermally coupled to an outlet stream of a butanedehydrator; and a second butane system heat source that comprises a heatexchanger that is thermally coupled to an outlet stream of a debutanizerbottoms.
 29. The method of claim 18, wherein the fourth portion of firstsub-units of the NGL fractionation plant comprises at least two naturalgasoline system heat sources, comprising: a first natural gasolinesystem heat source that comprises a heat exchanger that is thermallycoupled to an outlet stream of a natural gasoline decolorizer overheadstream; and a second natural gasoline system heat source that comprisesa heat exchanger that is thermally coupled to an outlet stream of a Reidvapor pressure control column overhead stream.
 30. The method of claim18, wherein the fifth portion of first sub-units of the NGLfractionation plant comprises at least two solvent regeneration systemheat sources, comprising: a first solvent regeneration system heatsource that comprises a heat exchanger that is thermally coupled to anoutlet stream of an ADIP regeneration section overhead stream; and asecond solvent regeneration system heat source that comprises a heatexchanger that is thermally coupled to an outlet stream of an ADIPregeneration section bottoms.
 31. The method of claim 18, wherein thefirst portion of second sub-units of the NGL fractionation plantcomprises at least one ethane system heat source, comprising: a firstethane system heat source that comprises a heat exchanger that isthermally coupled to an outlet stream of a deethanizer refrigerationcompressor.
 32. The method of claim 18, wherein the second portion ofsecond sub-units of the NGL fractionation plant comprises at least twopropane system heat sources, comprising: a first propane system heatsource that comprises a heat exchanger that is thermally coupled to anoutlet stream of a depropanizer overhead stream; a second propane systemheat source that comprises a heat exchanger that is thermally coupled toan outlet stream of a propane refrigeration compressor stream.
 33. Themethod of claim 18, wherein the third portion of second sub-units of theNGL fractionation plant comprises at least two butane system heatsources, comprising: a first butane system heat source that comprises aheat exchanger that is thermally coupled to an outlet stream of adebutanizer overhead stream; and a second butane system heat source thatcomprises a heat exchanger that is thermally coupled to an outlet streamof a butane refrigeration compressor stream.
 34. The method of claim 18,wherein the fourth portion of second sub-units of the NGL fractionationplant comprises at least one pentane system heat source, comprising: afirst pentane system heat source that comprises a heat exchanger that isthermally coupled to an outlet stream of a depentanizer overhead stream.35. The method of claim 18, wherein the fifth portion of secondsub-units of the NGL fractionation plant comprises at least one naturalgasoline system heat source, comprising: a first natural gasoline systemheat source that comprises a heat exchanger that is thermally coupled toan outlet stream of a natural gasoline decolorizing section pre-flashdrum overhead stream.